Studies of injection drug users (IDU) in drug treatment have shown elevated rates of co-morbid psychiatric disorders or symptoms, which likely present challenges to effective drug treatment and HIV/HCV risk reduction programs. However, many questions relevant to targeted treatment and risk reduction services for young IDU not in treatment, remain unanswered. We seek to better understand the relationships between injection drug use (IDU), psychiatric problems, service utilization, and HIV risk behavior, in order to form recommendations for targeted outreach and HIV-prevention programs for young IDUs. Our specific aims are: (1) to estimate the prevalence of psychiatric disorders and symptoms among young IDU;(2) to examine the sociodemographic and drug use correlates of psychiatric problems;(3) to identify gaps in access to psychiatric care, drug treatment, and HIV/STD prevention services among young IDUs with and without psychiatric problems;(4) to compare the rates of unsafe sex and injection behaviors among young IDUs with and without psychiatric problems;(5) to compare HIV-prevention knowledge, pro-prevention attitudes and norms, and self-efficacy for prevention behavior of young IDUs with and without psychiatric problems;and (6) to test an Information-Motivation-Behavioral Skills (IMB) model of HIV risk behavior on a sample of young IDUs. We will recruit 800 IDUs ages 18 to 25 years from Chicago neighborhoods through respondent driven sampling. Trained clinicians will administer the Psychiatric Research Interview for Substance and Mental Disorders (PRISM) to assess psychiatric disorders and symptoms. Respondents will also complete an ACASI survey to assess risk behavior, treatment and service history, socio-demographic background, and social-cognitive measures. Results of this study will provide (1) general prevalence estimates of psychiatric disorders among young IDU, (2) knowledge about gaps in access to psychiatric care, drug treatment, and prevention services, and (3) information about the relationships between psychiatric disorders and treatment/service utilization and HIV/HCV risk behaviors that may be informative to the design of future drug treatment and HIV/HCV prevention efforts that target young IDUs.